With the emergence of Software Defined Networks (SDN), new virtualization techniques have appeared. Traditional hypervision has attracted a lot of attention with respect to resource sharing and multi-tenancy. Cloud providers have usually a solid knowledge on how to manage computing, memory and storage resources, but often lack the ability to properly manage network resources. Thanks to OpenFlow, a widespread SDN southbound interface protocol, virtualizing the network infrastructure has become possible. However, network virtualization also comes with its own security issues. In this paper, we focus on the security aspects related to the migration of virtual networks. After providing a brief overview of the technological scope of our work, we review the state of the art of the migration of virtual resources. Finally, we conclude with our current results and the prospective outcomes we expect to obtain.